It makes me sad to see the posts from new mums asking AIBU in regards to their MILs and the perceived UB of these MIL, never do the mums refer to them as GMa.
Yes there is a distinction between their mums and DP/Hs mum but they are GMs.
I know all family relationships are not harmonious and we spend lots of time and effort accommodating each other but DC and GC bring such joy and miracles to families, so mums give MILs / GMs a bit of a break. Obviously not if they really are monsters!